Turbo_Ted
NAXJA Forum User
- Location
- Portland, OR
999 XJ Classic 4.0 automatic 4x4. Original engine broke #6 con rod.
Found a good replacement engine from a 1996. I swapped the various sensors from the 99 to the 96, so no harness modifications.
It cranks but doesn’t start. Starting fluid doesn’t do anything...no cough, no sputter. I have NOT tested fuel pressure, but the rail pressurizes enough to get a good squirt at the schrader valve. Pulling a plug reveals a very weak spark.
Disconnecting the crank position sensor changed it from a very weak spark to no spark. My son and I swapped the CPS anyhow. It is NOT a jeep sensor, but the behavior is the same...weak spark with it connected, no spark when disconnected.
I also replaced the coil with a Delphi...no change. The plugs, wires, cap, rotor, and plugs are all new.
Battery cables are new. Battery is new and fully charged. We cleaned the new cable ends and the body ground next to the battery, the ground at the coil bracket, and the wires grounding at the dipstick tube. The ground strap on the firewall is clean and attached to the intake manifold.
Any ideas?
I know there are sensor differences between the ‘96 and the ‘99...I don’t have any extra wires.
If it were a bmw motorcycle, I’d have it running in ten minutes. I’m just not as familiar with the Jeep ignition and what might prevent a nice, fat spark.
Found a good replacement engine from a 1996. I swapped the various sensors from the 99 to the 96, so no harness modifications.
It cranks but doesn’t start. Starting fluid doesn’t do anything...no cough, no sputter. I have NOT tested fuel pressure, but the rail pressurizes enough to get a good squirt at the schrader valve. Pulling a plug reveals a very weak spark.
Disconnecting the crank position sensor changed it from a very weak spark to no spark. My son and I swapped the CPS anyhow. It is NOT a jeep sensor, but the behavior is the same...weak spark with it connected, no spark when disconnected.
I also replaced the coil with a Delphi...no change. The plugs, wires, cap, rotor, and plugs are all new.
Battery cables are new. Battery is new and fully charged. We cleaned the new cable ends and the body ground next to the battery, the ground at the coil bracket, and the wires grounding at the dipstick tube. The ground strap on the firewall is clean and attached to the intake manifold.
Any ideas?
I know there are sensor differences between the ‘96 and the ‘99...I don’t have any extra wires.
If it were a bmw motorcycle, I’d have it running in ten minutes. I’m just not as familiar with the Jeep ignition and what might prevent a nice, fat spark.
